Am I correctly calculating the difficulty/XP for this encounter for a 15th-level party of 5 PCs?

I am putting together a campaign and have been experimenting with the guidelines for creating encounters and managing difficulty. I’ve done the math for quite a few encounters at each of the "tier" levels (5th, 11th, 15th) just to get a feel for how it works. One example is below. Does my method look correct?

15th level party, medium difficulty, 5 PCs  XP Threshold: 5(2800) = 14,000 xp 4 monsters so 2x Encounter Multiplier:  1 fire giant 1(2)(5000 xp) = 10000 xp 1 ogre       1(2)( 450 xp) =   900 xp 2 ettins     2(2)(1100 xp) =  4400 xp                              --------                              15300 xp 

So a wee bit more than the medium difficulty threshold but still less than the hard difficulty threshold. There are a lot of other factors to take into account when designing encounters and this is just back of the cocktail napkin math. A fire giant figures prominently in the campaign and I’m trying to figure out "when" to bring him in should it come to blows.